From: David Lebrun <david.lebrun@uclouvain•be>
To: Hannes Frederic Sowa <hannes@stressinduktion•org>,
<netdev@vger•kernel.org>
Subject: Re: [RFC PATCH net-next v2] ipv6: implement consistent hashing for equal-cost multipath routing
Date: Wed, 30 Nov 2016 08:56:54 +0100 [thread overview]
Message-ID: <583E8646.2010402@uclouvain.be> (raw)
In-Reply-To: <1480477952.3702850.803295033.367FD66D@webmail.messagingengine.com>
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On 11/30/2016 04:52 AM, Hannes Frederic Sowa wrote:
> In the worst case this causes 2GB (order 19) allocations (x == 31) to
> happen in GFP_ATOMIC (due to write lock) context and could cause update
> failures to the routing table due to fragmentation. Are you sure the
> upper limit of 31 is reasonable? I would very much prefer an upper limit
> of below or equal 25 for x to stay within the bounds of the slab
> allocators (which is still a lot and probably causes errors!).
> Unfortunately because of the nature of the sysctl you can't really
> create its own cache for it. :/
>
Agreed. I think that even something like 16 would be excessively
sufficient, that would enable 65K slices, which is way more than enough
to have sufficient balancing with a reasonable amount of nexthops (I
wonder whether there are actual deployments with more than 32 nexthops
for a route).
> Also by design, one day this should all be RCU and having that much data
> outstanding worries me a bit during routing table mutation.
>
> I am a fan of consistent hashing but I am not so sure if it belongs into
> a generic ECMP implementation or into its own ipvs or netfilter module
> where you specifically know how much memory to burn for it.
>
The complexity of the consistent hashing code might warrant something
like that, but I am ot sure of the implications.
> Also please convert the sysctl to a netlink attribute if you pursue this
> because if I change the sysctl while my quagga is hammering the routing
> table I would like to know which nodes allocate what amount of memory.
Yes, that was the idea.
Thanks for the feedback
David
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next prev parent reply other threads:[~2016-11-30 7:56 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-29 17:15 [RFC PATCH net-next v2] ipv6: implement consistent hashing for equal-cost multipath routing David Lebrun
2016-11-30 3:52 ` Hannes Frederic Sowa
2016-11-30 7:56 ` David Lebrun [this message]
2016-12-01 17:55 ` Roopa Prabhu
2016-12-02 8:29 ` David Lebrun
2016-11-30 4:04 ` Tom Herbert
2016-12-02 9:29 ` David Lebrun
2016-11-30 19:49 ` David Miller
2016-12-01 5:30 ` Hannes Frederic Sowa
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